1. Field of the Invention
The present invention relates to vacuum circuit breakers. More particularly, the present invention relates to circuit breakers having a mechanically interlocked grounding switch. Additionally, the present invention relates to circuit breakers for use in association with wind farm collection circuits.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Wind farms are becoming increasing popular for the generation of electricity. In a wind farm, there are a large number of wind energy generators installed in locations of the country where wind is consistent and substantial. Typically, the wind energy generators will include an array of blades that are coupled to a shaft. The rotation of the shaft caused by the rotation of the blades will produce electrical energy. Electrical lines will connect with the energy generator so as to deliver the energy from a particular wind energy generator to a collection bus. The electrical energy from the various wind energy generators in the wind farm can collectively pass energy to a substation.
Typically, these wind turbines can each produce between 500 kW and 3500 kW of power. The outputs of generators in the wind farm are often grouped into several electrical collection circuits. Transformers are used so as to tie the wind turbine output the conductors to the 34.5 kV collection circuits. The transformers serve to step up the output voltage of the wind energy generators to a medium voltage, usually 34.5 kilovolts. The various wind turbines in a wind farm are usually paralleled into collection circuits that can deliver 15 to 30 megawatts of power. In view of the voltage which has been stepped up to the 34.5 kilovolts, each collection circuit will require a circuit breaker rated at a minimum 34.5 kilovolts capacity. The energy will pass through the circuit breaker to the 34.5 kV bus of a substation. The 34.5 kV substation bus will go into one or more main step-up transformers and then tie into a high voltage utility line. As such, a need has developed so as to provide a circuit breaker that can tie collection circuits into the 34.5 kV substation bus. Such a circuit breaker should be of low cost, weatherproof, and able to effectively break the current in the event of a problem condition.
Typically, with circuit breakers, the circuit to the substation can be broken upon the application of a manual force to a button or lever of the circuit breaker or by an automatic relay which opens the circuit. Typically, the current is measured to the substation. If any relay senses a problem, then a signal is transmitted to the circuit breaker so as to open the breaker. Typically, the relays will be maintained within the substation. The opening of the circuit breaker will prevent the energy from being continued to be transmitted to the substation. Sometimes, the circuit breaker is open so as to allow users to work on the wind farm system, on the circuit breaker, or on the substation. Typically, the relays will operate if the sensors sense a voltage drop.
The interruption of electrical power circuits has always been an essential function, especially in cases of overloads or short circuits, when immediate interruption of the current flow becomes necessary as a protective measure. In earliest times, circuits could be broken only by separation of contacts in air followed by drawing the resulting electric arc out to such a length that it can no longer be maintained. This means of interruption soon became inadequate and special devices, termed “circuit breakers”, were developed. The basic problem is to control and quench the high power arc. This necessarily occurs at the separating contacts of a breaker when opening high current circuits. Since arcs generate a great deal of heat energy which is often destructive to the breaker's contacts, it is necessary to limit the duration of the arc and to develop contacts that can withstand the effect of the arc time after time.
A vacuum circuit breaker uses the rapid dielectric recovery and high dielectric strength of the vacuum. The pair of contacts are hermetically sealed in the vacuum envelope. An actuating motion is transmitted through bellows to the movable contact. When the electrodes are parted, an arc is produced and supported by metallic vapor boiled from the electrodes. Vapor particles expand into the vacuum and condense on solid surfaces. At a natural current zero the vapor particles disappear and the arc is extinguished.
In the past, various patents have issued relating to such vacuum circuit breakers. For example, U.S. Pat. No. 5,612,523, issued on Mar. 18, 1997 to Hakamata et al., teaches a vacuum circuit-breaker and electrode assembly. A portion of a highly conductive metal member is infiltrated in voids of a porous high melting point metal member. Both of the metal members are integrally joined to each other. An arc electrode portion is formed of a high melting point area in which the highly conductive metal is infiltrated in voids of the high melting point metal member. A coil electrode portion is formed by hollowing out the interior of a highly conductive metal area composed only of the highly conductive metal and by forming slits thereon. A rod is brazed on the rear surface of the coil electrode portion.
U.S. Pat. No. 6,048,216, issued on Apr. 11, 2000 to Komuro, describes a vacuum circuit breaker having a fixed electrode and a movable electrode. An arc electrode support member serves to support the arc electrode. A coil electrode is contiguous to the arc electrode support member. This vacuum circuit breaker is a highly reliable electrode of high strength which will undergoes little change with the lapse of time.
U.S. Pat. No. 6,759,617, issued on Jul. 6, 2004 to S. J. Yoon, describes a vacuum circuit breaker having a plurality of switching mechanisms with movable contacts and stationary contacts for connecting/breaking an electrical circuit between an electric source and an electric load. The actuator unit includes at least one rotary shaft for providing the movable contacts with dynamic power so as to move to positions contacting the stationary contacts or positions separating from the stationary contacts. A supporting frame fixes and supports the switching mechanism units and the actuator unit. A transfer link unit is used to transfer the rotating movement of the rotary shaft to a plurality of vertical movements.
U.S. Pat. No. 7,223,923, issued on May 28, 2007 to Kobayashi et al., provides a vacuum switchgear. This vacuum switchgear includes an electro-conductive outer vacuum container and a plurality of inner containers disposed in the outer vacuum container. The inner containers and the outer container are electrically isolated from each other. One of the inner vacuum containers accommodates a ground switch for keeping the circuit open while the switchgear is opened. A movable electrode is connected to an operating mechanism and a fixed electrode connected to a fixed electrode rod. Another inner vacuum container accommodates a function switch capable of having at least one of the functions of a circuit breaker, a disconnector and a load switch.
In the past, in association with such wind farms, when collect circuit breakers are opened, the collection circuit voltage would be interrupted and a transient overvoltage situation could occur in the collection circuit. In the over voltage situation, the high transient voltage in the collection circuit line will “back up” through the circuit and to the electronics associated with the wind energy generators. As a result, this transient overvoltage could cause damage to the circuitry associated with the wind energy generators and other circuitry throughout the system. As a result, in view of the characteristics of the large energy resident within by the overall wind energy farm, there is an extreme need to hold within acceptable limits any overvoltage which occurs when the circuit breaker is be opened.
Typically, to avoid the over voltage situation, grounding transformers have been required to be installed. These grounding transformers would typically have 34.5 kilovolts on the primary winding with a 600 volts open delta secondary winding. The transformer has a core with windings therearound. In view of the core and windings, there was continuous amount of core losses of energy associated with the use of such grounding transformers. Over time, the core losses could amount to a significant dollar amount of lost energy. Additionally, these grounding transformers had a relatively high initial cost, installation cost, and a long lead time of delivery.
FIG. 1 is an illustration of a prior art system employing a ground transformer. As can be seen, wind power generators 10, 12, 14 and 16 are connected respective lines 18, 20, 22 and 24 to a bus 26 via step-up transformers 17, 19, 21 and 23. The bus 26 has a switch 28 located therealong. The grounding transformer 30 is connected forwardly of the switch 28. When the switch 28 is opened, as illustrated in FIG. 1, the energy along the bus 26 is passed to the ground transformer 30 and to ground. When the switch 28 is closed, the energy from the bus 26 is passed along another bus 32 for passage to the circuit breaker 34 and then along line 36 to the substation 38. When the ground transformer 30 is effectively used, then any over voltages are immediately transferred to ground in an acceptable manner. As can be seen in FIG. 1, when the circuit breaker 34 is activated so as to open the circuit, a signal can be passed along line 40 to the switch 28 so as to open the switch 28 and to cause the energy in the bus 26 to pass to the ground transformer 30.
When ground transformers are not used, it is necessary to switch the circuit to ground extremely quickly. If the switch does not occur within a maximum of three cycles, then the overvoltage condition can occur. Ideally, to avoid any potential for an overvoltage situation, it is necessary to close the circuit to ground within one cycle, i.e. 16 milliseconds. Ultimately, experiments in attempting to achieve electrical switching systems indicated that the switching would occur at a level dangerously close to the five cycle limit. Preferably, it is desirable to cause the switching to occur in as close to an instantaneous manner as possible.
It is an object of the present invention to provide a vacuum circuit breaker with an integral high speed grounding switch of a relatively low cost.
It is another object of the present invention to provide a vacuum circuit breaker with an integral high speed grounding switch that is weatherproof.
It is a further object of the present invention to provide a vacuum circuit breaker with an integral high speed grounding switch which eliminates the need for ground transformers.
It is a further object of the present invention to provide a vacuum circuit breaker with an integral high speed grounding switch which minimizes energy losses.
It is still a further object of the present invention to provide a vacuum circuit breaker with an integral high speed grounding switch that closes the circuit to ground virtually instantaneously.
It is still a further object of the present invention to provide a vacuum circuit breaker with an integral high speed grounding switch that can be operated in the range of 34.5 kilovolts.
It is still another object of the present invention to provide a vacuum circuit breaker that is effective for use in association with wind farm energy production.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.